1. Field of the Invention
The present invention relates to color wheels for time-divisionally splitting white light ray emitted from a lamp light source into red, green and blue light rays, and relates to an optical projection apparatus and projection-type image displaying apparatus having the optical projection apparatus that emits colored light rays transmitted through the color wheels onto a reflection display device, and magnifies to project the image light rays formed on the reflection display device through a projection lens onto a screen.
2. Description of the Related Art
An optical system of a conventional optical projection apparatus includes: a lamp device for emitting white condensed light rays; a color wheel for inputting the condensed light from the lamp device and splitting the light into colored light rays in a time-divisional manner; a light mixing element for inputting the colored light rays transmitted through the color wheel and emitting from an output facet the light as a beam whose cross sectional illumination distribution is uniform; a relay lens for refracting the colored light rays emitted from the light mixing element; a digital micromirror device (hereinafter, referred to as a DMD) for inputting the colored light rays transmitted through the relay lens and reflecting image light rays after the light rays being modulated or switched in accordance with image signals; and a projection lens for magnifying and projecting the image light rays onto a screen (for example, refer to Patent Document 1). Here, the output facet of the light mixing element and the DMD are designed to have optically conjugate relationships. The color wheel used in the conventional optical system comprise three color (three primary colors; red, green, blue) or four color (add white color) filter segments having sector-like shapes and different color transmission characteristics with respect to light rays transmitting therethrough, and the wheel is configured in a disk form in which the filter segments are glued with each other. Here, the reason for the color wheel comprising at least three primary color filter segments is that since the color information of the colored light rays transmitted through the color wheel is uniform due to the nature of light, when a light spot in an arbitrary position on the color wheel is lapped along a circumferential direction on the color wheel, the circumferential integration value of the colored light rays transmitted through the point becomes white. Moreover, the reason for adding a white filter segment is that since the light transmitted through a white color filter segment has light quantity three times as much as the light rays transmitted through each of the three primary color segments, the four color filter segment is suited to improve visibility of white characters and to project images onto the screen in bright surroundings.
The conventional projection-type image displaying apparatus includes: the optical projection apparatus described above; a control unit for controlling rotation of a color wheel in synchronization with a frame rate of image signals inputted from outside; a sensor for outputting reference signals in synchronization with the rotation of the color wheel; a DMD control circuit for inputting the reference signals outputted from the sensor and controlling light modulation or switching process for the DMD; and a memory for inputting color data, which is corresponding to the color of colored light rays incident on the DMD, and transmitting the color data to the DMD based on the control signals from the DMD control circuit (for example, refer to patent document 2).
A method of projecting image based on image signals, which is inputted from outside, onto the screen using the projection-type image displaying apparatus configured as above has been proposed in that rotational velocity of the color wheel is controlled so as to synchronize the velocity with the frame rate, when the frame rate of the inputted image signals is detected. When white condensed light emitted from a lamp device is incident on three or four color filter segments on the color wheel in rotation, the condensed light transmitted through the color wheel is changed into a red light ray (hereinafter, referred to as “R”), a green light ray (hereinafter, referred to as “G”), a blue light ray (hereinafter, referred to as “B”), and a white light ray (hereinafter, referred to as “W”), which are split in time division based on distribution of each filter segment. The colored light rays split in time division are emitted from the light mixing element as a beam, whose cross-sectional illumination distribution is uniform, refracted by the relay lens, and then sequentially illuminate the DMD. At this time, if a reference signal is transmitted from the sensor in synchronization with the rotation of the color wheel, the DMD control circuit sequentially reads from the memory for color data of image signals corresponding to R, G, B, and W illuminating the DMD, based on the reference signal, and simultaneously transmits to the DMD control signals for light modulation or switching process. The DMD modulates or switches the colored light rays at an extremely high speed based on the control signals from the DMD control circuit, and reflects to the projection lens R, G, B, and W image light rays corresponding to the image signals. The R, G, B, and W image light rays, which are inputted from the DMD, are sequentially magnified and projected onto the screen by the projection lens. Here, if alternating rate of the colors is rapid enough, the colors are composed in viewer's brains and recognized as full-color images. Thereby, magnified images are projected onto the screen by using a spectrum effect of human eyes. Therefore, because the projection-type image displaying apparatus uses a spectrum effect of human eyes, it can be empirically concluded that the more splitting counts, that is, the shorter splitting time is, when the white light ray from the light source is split into R, G, and B light rays in time division, the more excellent the color display becomes.
Patent Document 1:
Japanese Laid-Open Open Patent Publications 2002-122805 (FIG. 1)
Patent Document 2:
Japanese Laid-Open Open Patent Publications 1997-054267 (FIG. 2)